Rolling bearing and production process therefor

ABSTRACT

A rolling bearing has an outer diameter surface of the outer ring which is a fitting surface with a housing and the inner diameter surface of the inner ring, which is a fitting surface with a shaft. The outer diameter surface of the outer ring or the inner diameter surface of the inner ring is coated with a bonded film containing an organic binder, a solid lubricant powder such as molybdenum disulfide powder, and a friction/wear modifier such as antimony oxide powder. According to the rolling bearing, a creep resistance is kept excellent without causing increase in cost and size and being deformed and softened.

TECHNICAL FIELD

The present invention relates to a rolling bearing that is to be used ina state where a raceway may creep relative to an opposite material suchas a housing.

RELATED ART

For a variety of rotating mechanical apparatuses, reduction in size andweight is required. Therefore, some rolling bearings have been made tobe thin. However, in a case of a rolling bearing in which an outer ringis fitted to a housing, when the outer ring is made to be thin, an outerdiameter surface of the outer ring is largely deformed due to a loadapplied from a rolling element, so that outer ring creep occurs. At thistime, the outer diameter surface of the outer ring and an inner surfaceof the housing are rubbed each other, so that wear occurs on thehousing. When the wear of the housing increases, a backlash occurs at arotation support part, so that abnormal vibration is generated and therotating mechanical apparatus is out of order.

In order to prevent the creep of the outer diameter surface of the outerring, for example, Patent Document 1 discloses that an axial shape ofthe outer diameter surface of the outer ring is formed to have anarc-shaped concave part, not a straight concave part. A bearing havingthe concave part formed on the outer diameter surface of the outer ringis press-fitted to the housing, and occurrence of the creep is preventedby interferences of both ends as large as possible. However, it isnecessary to press-fit the bearing to the housing with a high force, sothat the mounting is not easy.

In addition, a pin or a flange may be provided as a whirl stop. However,the number of components increases, and shapes of the bearing and thehousing become complicated, so that the processing cost and the sizeincrease. Furthermore, the operation of mounting the bearing to thehousing is troublesome, so that the manufacturing cost also increases.

Patent Document 2 discloses coating the outer diameter surface of theouter ring with a lubrication coating made of a thermosetting syntheticresin composition containing molybdenum disulfide, antimony and thelike. Since the lubrication coating has a lubricating property and isessentially made of resin, the lubrication coating is softer thanaluminum or aluminum alloy, which is a general material of the housing.Also, even when the creep occurs, it is possible to prevent the wear ofan inner peripheral surface of the housing. Also, since the lubricationcoating has only to be formed, it is possible to cope with a variety ofrolling bearings and the general versatility is also high. However,since the lubrication coating is obtained by applying a solution, inwhich the thermosetting synthetic resin composition containingmolybdenum disulfide and the like is dissolved in a solvent, and heatingthe solution to evaporate the solvent, the film strength and durabilitymay not be sufficiently secured.

Patent Document 3 discloses providing an O-ring on the outer diametersurface of the outer ring to fill a gap between the housing and thebearing and preventing the creep by a repulsive force of rubber formingthe O-ring. However, when unexpected expansion occurs in the housing,the repulsive force of rubber is decreased, so that the creep may occur.

Patent Document 4 discloses increasing a thickness of the outer ring toenhance the stiffness, thereby suppressing elastic deformation of theouter ring to prevent the creep. However, in order to completely preventthe creep, the thickness of the outer ring should be considerablyincreased, so that the size of the bearing is increased, which is notpreferable.

Patent Document 5 discloses coating a piston ring with a heat resistantresin containing molybdenum disulfide, antimony and the like. As theheat resistant resin, polyamideimide is used, and as a curing agent,phenol is used. However, since phenol is used as the curing agent, athermal curing treatment is performed at 180° C. to 220° C., in anembodiment. In a case of SUJ2 that is widely used for a bearing, since atempering temperature is about 120° C., the bearing may be deformed orsoftened at the high thermal curing temperature.

CITATION LIST Patent Documents

Patent Document 1: JP-A-H10-37967

Patent Document 2: JP-A-2002-266870

Patent Document 3: JP-A-2004-176785

Patent Document 4: JP-A-2012-241875

Patent Document 5: JP-A-H11-246823

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made in view of the above situations, andan object thereof is to implement a rolling bearing having aconfiguration in which an outer diameter surface of an outer ring is tobe fitted to a housing and a shaft is to be fitted to an inner diametersurface of an inner ring and capable of stably keeping an excellentcreep resistance for a long time, without causing increase in cost andsize. Also, an object of the present invention is to prevent a bearingfrom being deformed and softened when forming a bonded film forincreasing the creep resistance.

Means for Solving the Problems

In order to achieve the above objects, the present invention provides afollowing rolling bearing and a method of manufacturing the same.

(1) A rolling bearing including an outer ring, an inner ring, and arolling element rollably arranged between the outer ring and the innerring,

wherein at least one of an outer diameter surface of the outer ring andan inner diameter surface of the inner ring has a bonded film containingan organic binder comprising a base material and a curing agent, a solidlubricant powder, and a friction/wear modifier.

(2) The rolling bearing according to (1), wherein the curing agentcomprises an epoxy, an epoxy curing agent, or both the epoxy and theepoxy curing agent.

(3) The rolling bearing according to (1) or (2), wherein in a section ofthe bonded film, the friction/wear modifier having a cross-sectionalarea of 1 μm² or larger occupies an area ratio of 2.5% or greater.

(4) The rolling bearing according to one of (1) to (3), wherein the basematerial is polyamideimide,

wherein the solid lubricant contains a molybdenum disulfide powder andgraphite, and

wherein the friction/wear modifier contains an antimony oxide powder.

(5) The rolling bearing according to one of (1) to (4), wherein a valueobtained by dividing a mass of the solid lubricant by a mass of thefriction/wear modifier is larger than 0.7 and smaller than 1.8.

(6) A method of manufacturing a rolling bearing including an outer ring,an inner ring, and a rolling element rollably arranged between the outerring and the inner ring, the method including:

a process of applying a coating solution including an organic bindercomprising a base material and a curing agent, a solid lubricant powder,and a friction/wear modifier to at least one of an outer diametersurface of the outer ring and an inner diameter surface of the innerring, and

a process of thermal curing the coating solution.

(7) The method according to (6), wherein the curing agent comprises anepoxy, an epoxy curing agent, or both the epoxy and the epoxy curingagent, and

wherein the process of thermal curing is performed at 120° C. or lower.

Effects of the Invention

According to the rolling bearing of the present invention, the outerdiameter surface of the outer ring, which is a fitting surface with ahousing, or the inner diameter surface of the inner ring, which is afitting surface with a shaft, is coated with the bonded film containingthe organic binder, the solid lubricant powder such as molybdenumdisulfide powder, and the friction/wear modifier such as antimony oxidepowder. When polyamideimide is used as the base material of the organicbinder and epoxy is used as the curing agent, it is possible to form afilm at a tempering temperature or lower upon formation of the bondedfilm and to prevent the bearing from changing in size and beingsoftened. Also, the bonded film is softer than aluminum or aluminumalloy (for example, die-cast material), which is a general material ofthe housing. Therefore, even when the outer ring creep occurs and theouter diameter surface of the outer ring and the aluminum housing arerubbed each other, the aluminum housing is not worn. Also, since thebonded film has high wear resistance, the rolling bearing of the presentinvention can keep the excellent creep resistance for a long time.Furthermore, since the bonded film is simply formed on the outerdiameter surface of the outer ring or the inner diameter surface of theinner ring, the general versatility is high and the present inventioncan be applied to a variety of rolling bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view depicting an example of a rolling bearing ofthe present invention.

FIG. 2 is a pictorial view for illustrating a film structure on an outerdiameter surface of an outer ring.

FIG. 3 is a sectional view depicting an example of a transmission for anautomobile.

FIG. 4 is a photograph obtained by a scanning electron microscope,depicting an example of a section of the outer diameter surface of theouter ring.

FIG. 5 is a graph obtained in an embodiment, depicting a relationbetween a [(solid lubricant)/(friction/wear modifier)] ratio and a wearamount of a housing.

FIG. 6 is a graph obtained in an embodiment, depicting a relationbetween an area ratio of antimony oxide (Sb₂O₃) having a cross-sectionalarea 1 μm² or larger in a section of a bonded film and the wear amountof the housing.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail.

In the present invention, a type of the rolling bearing is not limited,and a ball bearing as shown in FIG. 1 is here exemplified. The ballbearing includes an outer ring 1 having an outer ring raceway 1 a, aninner ring 2 having an inner ring raceway 2 a, and a plurality of balls3 rollably arranged between both the raceways 1 a, 2 a. Also, an outerdiameter surface 1 b of the outer ring 1 of the ball bearing is fittedto a housing (not shown) and an inner peripheral surface of the innerring 2 is fitted to a shaft member (not shown).

The outer ring 1 and the inner ring 2 are made of metal. For example,SUJ2, SCM420, SCr420, SCR420, SUS440 or the like subjected to quenchingand tempering treatments or subjected to carburizing or nitrocarburizingtreatment and quenching and tempering treatments is used.

In the embodiment, the outer diameter surface 1 b of the outer ring 1 iscoated with a bonded film 5 containing an organic binder, a solidlubricant powder, and a friction/wear modifier. The housing is made ofaluminum or aluminum alloy (for example, aluminum die-cast material) forreducing in weight, in many cases. However, since the bonded film 5 ofthe present invention is softer than aluminum or aluminum alloy (forexample, aluminum die-cast material), the housing is not damaged eventhough the outer diameter surface 1 b of the outer ring and the housingis sliding contacted to each other.

The organic binder has high adhesiveness and wear resistance, so thatthe wear of the housing is small and a creep resistance wearcharacteristic is improved. The organic binder of the present inventionhas a curing agent mixed in a base material. Preferably, polyamideimideis used as the base material, and one or both of epoxy and epoxy curingagent is used as the curing agent. Polyamideimide and at least one ofthe epoxy and the epoxy curing agent are used, so that a treatment at atempering temperature (120° C.) or lower can be performed and a changein size due to deformation of the bearing and reduction in hardness dueto softening are not caused.

Although the epoxy is not particularly limited, bisphenol A type, cresolnovolac type, biphenyl type, brominated epoxy resin, alicyclic epoxyresin and the like may be exemplified. Also, although the epoxy curingagent is not particularly limited, aliphatic polyamine, polyaminoamide,polymercaptan, aromatic polyamine, acid anhydride, dicyandiamide and thelike may be exemplified. In the meantime, a curing promoter may betogether used so as to increase reactivity of the epoxy curing agent,and tertiary amine, tertiary amine salt, imidazole, phosphine,phosphonium salt, sulfonium salt and the like may be used.

The solid lubricant powder is required to have lubrication performanceand to be softer than aluminum or aluminum alloy, which is arepresentative material of the housing. As the solid lubricant,molybdenum disulfide is preferable. Molybdenum disulfide may be singlyused or may be used together with a solid lubricant, which is softerthan the material of the housing, such as graphite, tungsten disulfide,polytetrafluoroethylene (PTFE) and the like, as required. That is, thesolid lubricant powder is molybdenum disulfide powder or mixed powder ofmolybdenum disulfide powder and graphite and the like.

The wear/friction modifier is an additive for suppressing creep andimproving the wear resistance of the bonded film, and is preferably asolid material having hardness equal to or less than the housing.Specifically, a material having Hv 50 to 150 is preferable.Specifically, antimony oxide, tin, copper, zinc, nickel, talc, mica,potassium titanate and the like may be exemplified. Particularly,antimony oxide is preferable.

In order to form the bonded film 5, the organic binder dissolved in anappropriate solvent (for example, N-methyl-2-pyrrolidone (NMP), xyleneor the like) is added with predetermined amounts of powders of the solidlubricant (molybdenum disulfide, graphite, PTFE or the like) and powdersof the wear/friction modifier (antimony oxide), so that a coatingsolution is formulated. In order to uniformly mix/disperse the powdersin the coating solution, milling is performed with a ball mill or thelike. Then, the coating solution is applied to a workpiece (for example,the outer diameter surface 1 b of the outer ring 1) by dipping, sprayingor the like, and is baked for thermal curing in an oven such as athermostatic bath. During the thermal curing, the solvent is evaporated,so that a coating consisting of the organic binder and the powders (thesolid lubricant and the friction/wear modifier) is obtained after thethermal curing. The thermal curing temperature is 120° C. or lower whenpolyamideimide is used as the base material of the organic binder andepoxy is used as the curing agent, and the bearing can be prevented frombeing deformed and softened.

In the meantime, during the coating, a preheat treatment may beperformed so as to prevent non-uniformity and dripping due to abruptboiling of the solvent upon the baking. Also, in order to smoothen thesprayed film, a small amount (about 0.1%) of leveling agent may be addedto the solvent. An average particle diameter of the solid lubricantpowder and the raw material powder of the wear/friction modifier isappropriately 1 μm to 30 μm.

In the bonded film 5, a ratio (P/B) of the powders P comprising thesolid lubricant and the friction/wear modifier and the organic binder Bcomprising the base material and the curing agent is preferably0.43<(P/B)<2.3 by mass ratio. When the ratio (P/B) is smaller than 0.43,the powder components (the solid lubricant and the friction/wearmodifier) included in the bonded film 5 are too small, so that the solidlubrication action and the friction/wear modification action do notsufficiently function and the wear resistance of the bonded film 5 islowered. On the other hand, when the ratio (P/B) is greater than 2.3,the powder components included in the bonded film 5 are too much and anamount of the organic binder is relatively reduced. Therefore, thepowders cannot be anchored, so that it is not possible to keep the wearresistance of the bonded film 5 for a long time. More preferably, theratio is 0.67<(P/B)<1.5.

Also, a mixing ratio of the solid lubricant and the friction/wearmodifier has an optimal range, in which (solid lubricantamount/friction/wear modifier amount) is a value greater than 0.7 andsmaller than 1.8 by mass ratio, more preferably, 1.0 to 1.5. When themixing ratio of the solid lubricant is greater than 1.8, a ratio of thefriction/wear modifier, which is thought to mainly contribute to thewear resistance of the bonded film 5, becomes smaller, so that the wearresistance of the bonded film 5 is lowered. On the other hand, when themixing ratio of the solid lubricant is smaller than 0.7, a shear forceacting on a surface of the bonded film 5 becomes large, so that thebonded film 5 is likely to be worn.

Also, a particle diameter of the friction/wear modifier highlyinfluences the creep wear characteristic. Since the friction/wearmodifier bears a load to be applied to the bonded film 5, the larger thefriction/wear modifier is, the wear resistance of the bonded film 5 isimproved. Also, even though the surface of the bonded film 5 is worn,when the friction/wear modifier is large, the friction/wear modifier isnot simply detached from the bonded film 5 and stays in the film.Accordingly, the friction/wear modifier that is large to some extent ispreferably much contained in the bonded film 5, and an area ratio of thefriction/wear modifier having a cross-sectional area of 1 μm² or largerin a section of the bonded film 5 is preferably 2.5% or greater, andmore preferably 3% or greater. In the meantime, as described later, afilm thickness of the bonded film 5 is preferably 5 μm to 100 μm. If thearea ratio exceeds 15%, when the bonded film 5 is thin, specifically,the thickness of the bonded film 5 is about 10 μm, powder particlesequal to or larger than the film thickness exist, so that the surfacesmoothness of the bonded film 5 is deteriorated and the size precisionis not secured. For this reason, the area ratio is preferably 15% orless.

Meanwhile, in order to achieve the area ratio, the wear/frictionmodifier having the average particle diameter of 3 μm to 8 μm ispreferably contained in the bonded film 5, in an amount of 10 mass % to30 mass % to a total weight of the bonded film.

The film thickness of the bonded film 5 is preferably 5 μm to 100 μm.When the film thickness is smaller than 5 μm, the bonded film 5 is wornat an early stage and the creep wear resistance cannot be kept for along time. Also, it is difficult to uniformly form the bonded filmhaving the thin film thickness less than 5 μm. On the other hand, whenthe film thickness exceeds 100 μm, the film strength is lowered, so thatthe bonded film 5 may be peeled off. The film thickness is morepreferably 5 μm to 50 μm.

As a pretreatment for forming the bonded film 5, a phosphoric acidchemical conversion treatment is preferably performed. By the phosphoricacid chemical conversion treatment, the adhesiveness between the bondedfilm 5 and the outer diameter surface of the outer ring 1 b is enhanced.As phosphate that is used in the phosphoric acid chemical conversiontreatment, manganese phosphate, zinc phosphate, zinc calcium phosphate,iron phosphate and the like may be exemplified. A phosphate chemicalconversion coating is formed by the phosphoric acid chemical conversiontreatment. The phosphate chemical conversion coating has excellentadhesiveness with the outer diameter surface of the outer ring 1 b,concavity and convexity is formed on a surface thereof, and the bondedfilm 5 enters the concavity and convexity, so that the adhesiveness withthe bonded film 5 is also enhanced. For this reason, the outer diametersurface of the outer ring 1 b is difficult to be exposed, and the creepwear resistance is improved. Also, when the bearing steel is a materialthat cannot be subjected to the chemical conversion treatment, such asSUS440, the surface is roughened by shot blasting processing or thelike, so that the adhesiveness can be improved.

FIG. 2 pictorially depicts a section of the bonded film 5 formed byinterposing a chemical conversion coating on an outer diameter surfaceof the bearing. In the film, the powder-shaped solid lubricant (blackportions) and the wear/friction modifier (hatched portions) aredispersed and are bound by the organic binder. The respective actions ofthe solid lubricant and the wear/friction modifier are exhibited in abalanced manner, so that the favorable creep resistance is kept for along time.

From the above, the bonded film and the undercoating (pretreatment) ofthe present invention preferably have following configurations.

(1) The organic binder, the solid lubricant powder, and thefriction/wear modifier are contained.

(2) The organic binder includes epoxy and polyamideimide, and a contentof the organic binder is 40 mass % to 60 mass % of a total mass of thebonded film.

(3) The solid lubricant powder includes molybdenum disulfide andgraphite, a content of molybdenum disulfide to the total mass of thebonded film is 12 mass % to 34 mass %, and a content of graphite to thetotal mass of the bonded film is 2 mass % to 8 mass %.

(4) The friction/wear modifier includes antimony oxide, and a contentthereof is 15 mass % to 30 mass % to the total mass of the bonded film.

(5) The area ratio of the friction/wear modifier having across-sectional area 1 μm² or larger is 3% or greater in the section ofthe bonded film.

(6) A value obtained by dividing mass of the solid lubricant by mass ofthe friction/wear modifier is 1 to 1.5.

(7) The film thickness of the bonded film is 5 μm to 50 μm.

(8) As the undercoating, a chemical conversion film including phosphoricacid is provided.

In the embodiment, the ball bearing has been exemplified. However, thepresent invention is not limited thereto. For example, the presentinvention can be applied to the other rolling bearings such as acylindrical roller bearing, a tapered roller bearing, and the like.Also, since the bonded film is simply formed on the outer diametersurface of the outer ring, it is possible to easily cope with a varietyof bearings.

Also, as a utility in which the outer ring 1 of the rolling bearing isto be fitted to the housing, a transmission for an automobile may beexemplified. FIG. 3 is a sectional view depicting an example thereof, inwhich a shaft member 50 is arranged inside a housing 40 and the shaftmember 50 is rotatably supported by a plurality of rolling bearings. Inthe meantime, the shaft member 50 is configured by two members 50A, 50B.The rolling bearing includes an outer ring 10, an inner ring 20, and aplurality of balls 30 rollably arranged between respective raceways 10a, 20 a, an outer diameter surface 10 b of the outer ring 10 is fittedto an inner peripheral surface 40 b of the housing 40 by interferencefitting or the like, and an inner diameter surface 20 b of the innerring 20 is fitted to an outer peripheral surface 50 b of the shaftmember 50 by interference fitting or the like. According to the presentinvention, the outer diameter surface 10 b of the outer ring 10 of therolling bearing is formed with the bonded film 5 for preventing thewear.

In addition, the present invention can be applied to a general rollingbearing having a structure where the outer diameter surface of the outerring is to be fitted to the housing.

Also, when the creep is to be caused in the inner ring and a shaft, thebonded film of the present invention may be formed on the inner diametersurface of the inner ring 2.

Embodiments

In the below, the present invention will be further described withreference to test examples. However, it should be noted that the presentinvention is not limited thereto.

(Embodiment 1, Comparative Example 1)

In this test, the effects that are to be accomplished by the bonded filmof the present invention was verified.

As shown in Table 1, the organic binder comprising epoxy andpolyamideimide, molybdenum disulfide powders (“MoS₂” in Table), antimonyoxide powders (“Sb₂O₃” in Table), graphite powders (“C” in Table) weredispersed in N-methyl-2-pyrrolidone in the shown amounts, so that thecoating solution was formulated. Also, the average particle diameter ofthe raw material powders of molybdenum disulfide was set to 3 μm, andthe average particle diameter of the raw material powders of antimonyoxide was set to 8 μm. As the undercoating treatment, a chemicalconversion coating of manganese phosphate was formed, and the coatingsolution was applied to the outer diameter surface of the outer ring ofthe test bearing, which was then thermal cured at 120° C. for 30 minutesto form the bonded film. The film thickness of the bonded film was setto 15 μm.

FIG. 4 depicts an example of a SEM (Scanning Electron Microscope)photograph of the bonded film of Embodiment 1. In the photograph,platinum coating was performed for SEM observation. Also, in thephotograph, molybdenum disulfide powder is denoted as “Mo”, and antimonyoxide powder is denoted as “Sb”. From the photograph, it can be seenthat molybdenum disulfide powders and antimony oxide powders aredispersed in the bonded film.

For the test bearing (Embodiment 1) having the bonded film formedthereon and a test bearing (Comparative Example 1) with no bonded film,a bearing test was performed with a following condition 1 in a statewhere the outer ring was fitted to the housing made of aluminum alloy,so as to evaluate a creep wear amount of the housing. In the meantime,the creep wear amount was obtained from a weight difference of thehousing before and after the test.

<Bearing Test Condition 1>

-   -   test bearing: deep groove type bearing (outer diameter 39 mm,        inner diameter 17 mm)    -   bearing material: bearing steel (SUJ2)    -   housing: aluminum alloy    -   test radial load: 3577N    -   inner ring revolution: 3900 min⁻¹    -   atmosphere: CTV fluid, forced supply lubrication    -   test temperature: 100° C.    -   hour: 48 hours    -   evaluation items: wear amount of housing

The results are shown in Table 1. In the results, the value is describedwhen the creep wear amount of Comparative Example 1 is set to 1.

TABLE 1 Powders Binder Total amount MoS₂ C Sb₂O₃ amount (P) amountamount amount (B) Creep wear (mass %) (mass %) (mass %) (mass %) (mass%) amount Embodiment 1 50 25 5 20 50 0.05 Comparative No chemicalconversion treatment film and bonded film 1 Example 1

It can be seen that the creep wear is smaller in the bonded film of thepresent invention.

(Embodiments 2 and 3, Comparative Examples 2 to 4)

In this test, in order to examine an influence of the friction/wearmodifier (antimony oxide) included in the bonded film, the test bearinghaving the bonded film of the composition shown in Table 2 was evaluatedwith the above condition 1. Also, the average particle diameter of theraw material powders of molybdenum disulfide was set to 3 μm, and theaverage particle diameter of the raw material powders of antimony oxidewas set to 1 μm. In the meantime, as the undercoating treatment, thechemical conversion treatment using manganese phosphate was performed,and polyamideimide was used as the organic binder and the epoxy was usedas the curing agent. Also, the film thickness of the bonded film was setto 15 μm. The results are shown by a relation of the [(solidlubricant)/(friction/wear modifier)] ratio and the housing wear amount,in Table 2. The wear amount of the housing is shown by the weight ratiowhen Comparative Example 2 is set to 1. The small value thereofindicates that the wear of the housing due to the creep phenomenon issmall.

TABLE 2 [(solid Powders Binder lubricant)/ Total amount MoS₂ C Sb₂O₃amount (friction/wear Housing (P) amount amount amount (B) modifier)]wear (mass %) (mass %) (mass %) (mass %) (mass %) ratio amountComparative 50 45 5 0 50 — 1.0 Example 2 Comparative 50 29 5 16 50 2.20.35 Example 3 Comparative 50 13.5 5 31.5 50 0.6 0.5 Example 4Embodiment 2 50 25 5 20 50 1.5 0.1 Embodiment 3 50 20 5 25 50 1.0 0.1notes) the solid lubricant amount is a sum amount of MoS₂ and C.

Also, the similar test was performed with a following condition 2. Theresults are shown with a graph in FIG. 5. It can be seen that the wearamount of the housing changes due to the influence of the [(solidlubricant)/(friction/wear modifier)] ratio. From Table 2 and FIG. 5, itcan be seen that the [(solid lubricant)/(friction/wear modifier)] ratiohas an optimal range and that within a range greater than 0.7 andsmaller than 1.8, the housing wear amount is considerably reduced andthe wear due to the creep is reduced, as compared to Comparative Example2 in which only the solid lubricant is included and the friction/wearmodifier is not included. The more preferable range of the [(solidlubricant)/(friction/wear modifier)] ratio is 1.0 to 1.5, in which thewear amount is reduced by about 10%, as compared to Comparative Example2.

<Bearing Test Condition 2>

-   -   test bearing: deep groove type bearing (outer diameter 53 mm,        inner diameter 30 mm, thickness: 13 mm)    -   bearing material: bearing steel (SUJ2)    -   housing: aluminum alloy    -   test radial load: 7300N    -   inner ring revolution: 3900 min⁻¹    -   atmosphere: FBK oil RO 68 available from JX Nippon Oil, forced        supply circulation    -   test temperature: about 100° C.    -   hour: 48 hours    -   evaluation items: wear amount of housing

When the amount of the solid lubricant is large in the bonded film, theratio of the friction/wear modifier, which is thought to mainlycontribute to the wear resistance of the bonded film, becomes smaller,so that the wear resistance of the bonded film is lowered. On the otherhand, when the amount of the solid lubricant is small, a shear forceacting on the surface of the bonded film becomes large, so that thebonded film is likely to be worn. Accordingly, it is thought that themixing ratio between the solid lubricant and the friction/wear modifierhas the optimal value as described above.

(Embodiments 4 and 5, Comparative Examples 5 and 6)

In this test, an influence of the particle diameter of the friction/wearmodifier included in the bonded film was examined.

Before examining the influence of the particle diameter, it was examinedhow to define the particle diameter of the friction/wear modifier to bedispersed in the bonded film. Basically, a section of the bonded film isobserved by a scanning electron microscope (SEM), and the elements areidentified by an energy dispersive X-ray spectroscopy (EDX) attached tothe scanning electron microscope. A sample is manufactured by cuttingthe outer diameter surface of the outer ring having the bonded filmcoated thereon, embedding the same in a resin and grinding a surfacethereof. At this time, platinum coating is performed for the SEMobservation.

FIG. 4 (Embodiment 1) depicts an example of the section observation ofthe bonded film. In FIG. 4, the elements identified by the EDX areshown. In FIG. 4, Mo indicates MoS₂, and Sb indicates Sb₂O₃. As shown,MoS₂ has an elongated shape, Sb₂O₃ has a polygonal or circular shape,and MoS₂ and Sb₂O₃ are dispersed in the bonded film. In this example, asthe raw material powder, antimony oxide having an average particlediameter of 8 μm was used. As can be seen from FIG. 4, the particlediameter of antimony oxide in the bonded film is smaller than theaverage particle diameter of the raw material powders. The reason isthat when formulating the coating solution, which is a raw material ofthe bonded film, the milling process was performed. For this reason, itis not possible to define the particle diameter of antimony oxide in thebonded film by the average particle diameter of the raw materialpowders. Also, it is actually impossible to obtain the particle diameterof antimony oxide in the bonded film because it is necessary to performthe identification for the very small particles.

Therefore, a section of the bonded film is observed, and a ratio (Sb₂O³area ratio), which indicates that antimony oxide having across-sectional area of 1 μm² or larger occupies in the section of thebonded film, is used. The large value thereof indirectly means that theparticle diameter of antimony oxide in the bonded film is large. A totalarea of the particles having a cross-sectional area of 1 μm² or largeris calculated using the particle analysis of image analysis software(ImageJ). At this time, molybdenum disulfide powders and antimony oxidepowders in the bonded film are extracted by binarization of an image ora setting of roundness. When a result thereof is different from theresult of the EDX, a following method is performed. First, a section ofthe bonded film is photographed, and particles to be extracted in thephotograph are compactly colored with ink. Then, the photograph is readby a scanner, and the image analysis is performed for the data.According to the particle analysis performed for FIG. 4 by the abovemethod, the area ratio of antimony oxide powders included in the sectionof the bonded film and having a cross-sectional area of 1 μm² or largerwas 3.1%. In the meantime, the area ratio of molybdenum disulfidepowders included in the section of the bonded film and having across-sectional area of 1 μm² or larger can also be calculated by asimilar method.

During the test, in Embodiment 2, the area ratio of antimony oxidepowders in the bonded film was changed by changing the average particlediameter of the raw material powders of antimony oxide to be added. Thatis, as the undercoating treatment, the chemical conversion treatmentusing manganese phosphate was performed, polyamideimide was used as theorganic binder, the epoxy was used as the curing agent, the averageparticle diameter of the raw material powders of molybdenum disulfidewas unchanged and the average particle diameter of the raw materialpowders of antimony oxide was changed, so that the bonded film wasformed on the test bearing. The film thickness of the bonded film wasset to 15 μm. Table 3 shows the average particle diameter of the rawmaterial powders of molybdenum oxide and the area ratio of antimonyoxide powders having a cross-sectional area of 1 μm² or larger in thebonded film.

The housing wear amount was measured using the test bearing, inaccordance with a following condition 3. The results are shown in Table3 and FIG. 6. In the meantime, the wear amount of the housing isindicated by a relative value when the wear amount of ComparativeExample 6 is set to 1. The small value thereof means that the wear ofthe housing due to the creep phenomenon is small.

<Bearing Test Condition 3>

-   -   test bearing: deep groove type bearing (outer diameter 53 mm,        inner diameter 30 mm, thickness: 13 mm)    -   bearing material: bearing steel (SUJ2)    -   housing: aluminum alloy    -   test radial load: 7300N    -   inner ring revolution: 3900 min⁻¹    -   atmosphere: Nissan CVT fluid NS-3, forced supply circulation    -   test temperature: about 100° C.    -   hour: 48 hours    -   evaluation items: wear amount of aluminum housing when the outer        ring is rotated by 250 revolutions by the creep

TABLE 3 average particle diameter Sb₂O₃ of raw material powders housingwear area ratio (μm) amount (%) Comparative 0.1 1.8 0.0 Example 5Comparative 1 1.0 1.6 Example 6 Embodiment 4 3 0.6 2.5*¹ Embodiment 5 80.5 3.4 *¹the value obtained by an approximate equation (approximateequation: y = 0.77ln(x) + 1.7) when the average particle diameter of theraw material powders of Comparative Example 5, Comparative Example 6 andEmbodiment 5 is denoted with x and Sb₂O₃ area ratio is denoted with y.

From the results, it can be seen that the larger the area ratio ofantimony oxide powders is, the wear amount of the housing is reduced. Asone reason, it is thought that since the antimony oxide powders bear aload to be applied to the bonded film, the antimony oxide powders, whichare large to some extent, in the film improved the wear resistance ofthe bonded film. Also, another reason, it is thought that even thoughthe surface of the bonded film is worn, when the antimony oxide powdersare large to some extent, the antimony oxide powders stay in the filmwithout being detached from the bonded film. Therefore, the area ratioof antimony oxide having a cross-sectional area of 1 μm² or larger inthe section of the bonded film is preferably 2.5% or greater, and morepreferably 3% or greater. The area ratio of antimony oxide is preferablygreater. However, if the area ratio exceeds 15%, when the bonded film isthin, for example, the thickness of the bonded film is about 10 μm,powder particles equal to or larger than the film thickness of thebonded film exist, so that the surface smoothness of the bonded film isdeteriorated and the size precision is not secured. For this reason, thearea ratio of antimony oxide is preferably 15% or less.

Also, when comparing the time consumed to reach the predeterminedrevolutions (for example, 250 revolutions), it was confirmed that thelarger antimony oxide (the greater area ratio) requires the longer time.That is, it is thought that the size of antimony oxide suppresses thecreep itself.

Meanwhile, the molybdenum disulfide powders were also examined withrespect to the influence of the average particle diameter of the rawmaterial powders thereof by changing the average particle diameter (3μm, 16 μm). However, it was checked that there was no substantialinfluence. That is, since the solid lubricant reduces the shear forceacting on the surface of the bonded film, it is thought that the solidlubricant contributes to the improvement on the wear resistance of thebonded film. However, it is guessed that this action is not influencedby the particle diameter.

From the above results, it can be seen that it is possible to reduce thecreep wear by the bonded film of the present invention.

Although the present invention has been described in detail withreference to the specific embodiments, it is obvious to one skilled inthe art that a variety of changes and modifications can be made withoutdeparting from the spirit and scope of the present invention.

The subject application is based on Japanese Patent Application Nos.2016-165994 filed on Aug. 26, 2016 and 2017-153165 filed on Aug. 8,2017, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The rolling bearing of the present invention has the excellent creepresistance, and is useful for a utility that is to be used in a statewhere the raceway may creep relative to the opposite material such as ahousing, for example, for a rolling bearing that is to be used for atransmission for an automobile.

DESCRIPTION OF REFERENCE NUMERALS

1: outer ring

1 a: outer ring raceway

1 b: outer diameter surface

2: inner ring

2 a: inner ring raceway

3: ball

5: bonded film

The invention claimed is:
 1. A rolling bearing including an outer ring,an inner ring, and a rolling element rollably arranged between the outerring and the inner ring, wherein an outer diameter surface of the outerring is configured to be fitted to a first member, an inner diametersurface of the inner ring is configured to be fitted to a second member,and the first member and the second member are rotatable relative to oneanother, wherein at least one of the outer diameter surface of the outerring and the inner diameter surface of the inner ring has a bonded filmcontaining an organic binder comprising a base material and a curingagent, a solid lubricant powder, and a friction/wear modifier, whereinin a section of the bonded film, the friction/wear modifier having across-sectional area of 1 μm² or larger occupies an area ratio of 2.5%or greater, wherein the solid lubricant contains a molybdenum disulfidepowder and graphite, and wherein the friction/wear modifier contains anantimony oxide powder.
 2. The rolling bearing according to claim 1,wherein a value obtained by dividing a mass of the solid lubricant by amass of the friction/wear modifier is larger than 0.7 and smaller than1.8.
 3. The rolling bearing according to claim 2, wherein the basematerial is a polyamideimide, and wherein the curing agent comprises anepoxy, an epoxy curing agent, or both the epoxy and the epoxy curingagent.
 4. The rolling bearing according to claim 1, wherein the basematerial is a polyamideimide, and wherein the curing agent comprises anepoxy, an epoxy curing agent, or both the epoxy and the epoxy curingagent.
 5. A method of manufacturing a rolling bearing including an outerring, an inner ring, and a rolling element rollably arranged between theouter ring and the inner ring, wherein an outer diameter surface of theouter ring is configured to be fitted to a first member, an innerdiameter surface of the inner ring is configured to be fitted to asecond member, and the first member and the second member are rotatablerelative to one another, and wherein the method including: a process ofapplying a coating solution including an organic binder comprising abase material and a curing agent, a solid lubricant powder, and afriction/wear modifier to at least one of the outer diameter surface ofthe outer ring and the inner diameter surface of the inner ring, and aprocess of thermal curing the coating solution; wherein in a section ofthe bonded film, the friction/wear modifier having a cross-sectionalarea of 1 μm² or larger occupies an area ratio of 2.5% or greater,wherein the solid lubricant contains a molybdenum disulfide powder andgraphite, and wherein the friction/wear modifier contains an antimonyoxide powder.
 6. The method according to claim 5, wherein the basematerial is a polyamideimide, and wherein the curing agent comprises anepoxy, an epoxy curing agent, or both the epoxy and the epoxy curingagent.
 7. The method according to claim 5, wherein the coating solutionis thermal cured at 120° C. or lower.
 8. The method according to claim5, wherein a value obtained by dividing a mass of the solid lubricant bya mass of the friction/wear modifier is larger than 0.7 and smaller than1.8.